The air compressor is an important equipment in various industrial enterprises, mining and construction industries. Its main function is to provide continuous and pressure-bearing compressed air for automatic production equipment, such as supplying air to the injection molding machine to ensure its normal operation. Production of plastic products. There are many types of air compressors, such as screw air compressors, piston air compressors, centrifugal air compressors, scroll air compressors, etc., which are widely used in many industries.

In this paper, the problem of the lack of self-diagnosis and monitoring capability of the relay air compressor control system is discussed. The control system design solution based on the PLC platform is discussed.

2 Air compressor system analysis 2.1 Process flow In the air compressor control system, the pressure sensor installed on the air outlet pipe of the air compressor back end is used to control the pressure of the air compressor. When the air compressor is started, the loading solenoid valve is in the closed state, the loading cylinder does not operate, and the inverter drives the motor to run at no load for a period of time (the controller can be arbitrarily set, generally set to ls), and the loading solenoid valve is opened. The air compressor is running on load. When the air compressor starts running, if the back-end equipment uses a large amount of gas, and the pressure of the compressed gas in the gas storage tank and the rear-end pipeline does not reach the upper pressure limit, the controller acts to load the valve, open the intake port, and the motor load Run, continuously producing compressed air to the rear line. If the gas is stopped by the gas equipment at the back end, the pressure of the compressed gas in the rear end pipeline and the gas storage tank gradually increases. When the pressure upper limit value is reached, the pressure sensor sends an unloading signal, and the loading solenoid valve stops working, the air inlet The filter is turned off and the motor is running at no load.

When the air compressor is running continuously, the temperature of the compressor main body will rise. When the temperature reaches a certain level (generally set to 80 °C, the controller can be set according to the application environment), the fan starts running, and the sub-lowering machine works. temperature.

Control insurance to help the loop grapefruit pressure protection water pressure protection shoulder movement constitution string when the oil pressure report sleeve pressure low sister when the grapefruit pressure normal water pressure low JBE water pressure iE often pumping low sister when the parking water pressure is low when parking thermal protection The operation instruction is to tear the orange to the action, and the 1ZJ is closed to the thermal protection system to achieve normal operation. If the hydraulic pressure is not normal at the start, it cannot be started; if the thermal protection action, oil pressure and water pressure protection action occur during normal operation of the system Then a trip action is generated.

At the same time, it can be seen that the system uses a conventional relay chain system, and the system mechanism is more complicated.

The electric control system of the air compressor adopts the conventional relay mode without system fault indication. The electrical equipment is aging, the line is chaotic, the instrument system is complicated, which makes the equipment management complicated and difficult. The traditional control system has higher requirements for circuit operation, and the faulty fan runs for a period of time. The host temperature drops and cannot be eliminated for a short time. In its control, the fan is stopped by loading below 75 °C. The air compressor process is as shown.

The functions of the air compressor control system are summarized in four aspects: automatic adjustment of the displacement of the compressor to keep the pressure of the gas storage tank within the set range; in the temperature control system, the fan motor is automatically stopped and started, so that the fan motor is automatically stopped and started. The head exhaust temperature is kept within the set range; in the event of over temperature, over pressure, over current, etc., alarm or stop; in the start and stop, according to the set timing to open and close the electrical components 2.2 relay electronic control system analysis tradition The control system circuit is as shown. Through the analysis, the working principle is known: when the air compressor starts, press the start button SB2, the hydraulic pressure water pressure starts normally, the circuit is turned on, the 1C AC contactor is closed, the AC contactor is closed, the motor is opened, the valve is unloaded to control the air pressure. The gas supply of the machine causes the gas consumption to fluctuate due to the working cycle of the gas equipment or the difference in the production process, which sometimes causes the air compressor to be frequently loaded and unloaded. After the air compressor is unloaded, it still runs at the power frequency, which not only wastes electric energy but also increases the mechanical wear of the equipment, and the loading is a sudden process, which will cause a great impact on the equipment and the power grid. Therefore, the frequency conversion transformation of the air compressor has the effects of improving the starting and running of the motor, reducing the mechanical wear of the equipment, and saving electric energy within a certain range.

3PLC Solution Design 3.1 General Requirements of Control System The air compressor adopts PLC control system, which should meet the following requirements: (1) The power supply of the whole control system is AC/DC online switching to ensure PLC data processing and control in abnormal situations ( Including power conversion) can work reliably; temperature signal feedback as a criterion to achieve PLC control start and stop air compressor; central processing module, communication module, power module, analog module, etc., all modules are plug-in split The structural components meet the above industrial control level; according to the pressure of the pressure collection signal (gas tank pressure P1, P2, P3, P4), the main and secondary air compressors are automatically started; each air compressor works for 30 minutes and starts. The sewage valve is 15 seconds; all the start-stop air compressors and abnormal signals are sent to the HMI for processing; (5) meet the industrial production site operating conditions, with high reliability and strong anti-interference performance.

3.2 Control system hardware design According to the system control requirements, it is proposed to adopt dual redundant design, that is, use two air compressors, and the two air compressors are mutually standby. Externally equipped with detection components, analysis components, actuators and human-machine interface. The air compressor testing components include temperature sensor, pressure switch, differential pressure switch, etc.; the analysis component is mainly PLC; the actuator has a loading solenoid valve, a venting solenoid valve, and a contactor; the human-machine interface is mainly a MCGSTPC touch screen, buttons and signal lights.

The principle design based on the Japanese Omron PLC control system is as shown. The circuit control principle in the PLC control box is as shown. The flow chart design is as shown.

Air compressor control system structure main sticker "Slave Atttt electricity 31 from the study of electricity * wood pressure low PLC programming process established by the main control window, device window, user window, real-time database and operating strategy consists of five parts, each Some of them are configured separately to perform different tasks and have different characteristics.

It is an independent running system, which performs various processing according to the method specified by the user in the configuration environment, and completes the goals and functions of the user configuration design.

According to the different operators, set different usage rights, effectively ensure the system 3.3 system debugging into the wiring of the power line and control line, pay attention to the peripheral options of the inverter (such as: open, circuit breaker, reactor, etc.) The connection and the wire diameter and material of the power line used; the parameter of the device and the configuration of the man-machine interface; whether it is in normal operation; if there is a fault, the fault is removed according to the specific fault phenomenon until the device can operate normally; (4) The device is operating normally. After that, according to the actual gas demand, adjust the appropriate outlet pressure, and the operating current fluctuates within a small range (several amps or less), the parameters related to current fluctuation, controller P, I, D parameters, etc. Can be adjusted according to the actual situation.

Monitoring and Display This system realizes real-time monitoring of all parameters of air compressor operation through MCGS configuration software, so that the current flow, power supply parameters, monitoring temperature, monitoring pressure and other visual dynamics of each air compressor are displayed on the same screen. It is convenient for monitoring production and real-time management of the production process and visualization of the system.

Parametric over-limit alarm and fault diagnosis This project sets an over-limit alarm for the main current, cylinder exhaust temperature, oil temperature, wind package temperature, cooling water temperature, cylinder pressure, oil pressure, water cut and other parameters of the air compressor system. Once the parameter value exceeds the limit during the running process, the configuration software can realize the classified voice alarm and dynamic screen prompt, and can store the alarm information in the alarm information database for post-statistical analysis. For each parameter with alarm attribute set, the reason analysis is given during configuration. Therefore, the fault information diagnosis database can be generated by the report information database for on-site personnel inspection. According to the regulations, the reporting limits of different parameters of the air compressor system vary from season to season. To adapt to this situation, the online setting of the alarm limits is realized by the circulation strategy.

Save data processing The historical report and historical curve set by MCGS configuration software are used to display the running status and change trend of the key parameters of the air compressor at any time in the history in the form of graphs or curves, so as to be used for on-site controllers for query and analysis. The class report, the æ›° report, and the monthly report produced by the save data extraction and the Excel report output component can be periodically printed and reported, which overcomes the cumbersome and random nature of the previously manually recorded data.

5 Conclusion After the on-site adjustment test, this equipment has been running on the site for more than one year, and it is reliable in operation, which plays an important role in the safe and stable operation of the company's production.

The PLC-based air compressor control system is safe and reliable, with high intelligence, good real-time adjustment, friendly human-machine interface, effectively overcomes the unfavorable factors such as adjustment lag caused by human factors, and is easy to operate and can be unattended. .

In the implementation process of the control system, the fault detection and fault diagnosis processing procedures can also be introduced, which can improve the intelligence degree of the system and help to further improve the effectiveness and reliability of the control system. By optimizing the application of automatic control functions such as scheduling strategy and software chain protection, the automatic touch will be further raised to a higher level, which provides a strong reference for other devices.

Professor, now working in Wuxi Communication Higher Vocational Technical School in Jiangsu Province, the main research direction is automatic control of industrial process

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